1. Field of the Invention
The present invention relates to an interpupillary distance adjustment mechanism for an optical device, and particularly to an interpupillary distance adjustment mechanism that is manually operable during use of the optical device.
2. Description of Prior Art
A laser rangefinder is one of the main optical devices for distance measurement. A common type of laser rangefinder usually applies a laser emitter as a light source for transmitting a modulated laser light beam to a target object to be measured. The target object reflects and returns the laser light beam to a laser receiver. The distance to the target object is determined by multiplying the light velocity by the time interval between emission of the laser beam and the receipt of the reflected beam, and can be expressed as: L=C*Td/2, wherein “L” represents the distance between the target object and the laser rangefinder, “C” represents the light velocity, and “Td” is the time interval between the emission of the laser beam and the receipt of the reflected beam. Since the light velocity “C” is a constant, so long as the time interval “Td” between the emission of the laser beam and the receipt of the reflected beam is accurately measured, the accurate distance to the target object can be obtained.
Similar to telescopes, laser rangefinders are classified as monocular and binocular laser rangefinders. Generally, a monocular laser rangefinder is much less expensive, has higher magnification power, and can be hand-held or tripod mounted for viewing. However, the monocular laser rangefinder is generally very long in size, which is inconvenient for carry. Further, monocular viewing of the target object is much more tiring for the human eye than binocular viewing. In contrast, a binocular laser rangefinder allows the user to view binocularly, and can be made smaller for easy carrying and hand-held viewing. These make the binocular laser rangefinder more useful in various applications.
Since the eye separation in humans varies greatly, the binocular laser rangefinder necessitates mechanism for adjusting the difference in interpupillary distance. Conventionally, the interpupillary distance may be adjusted by swivel action to change the distance between two lens barrels, such as those disclosed in U.S. Pat. Nos. 5,973,830 and 6,667,833. Alternatively, the interpupillary distance may be adjusted by sliding and thus moving the two lens barrels toward or away from each other, such as those disclosed in U.S. Pat. Nos. 5,444,568, 5,633,753, 5,734,499, and 6,236,504.
The swivel action is generally applied to binocular telescopes. However, it has the disadvantage that miniaturization design is difficult.
Therefore, for compact designs, the sliding action is preferred. Whether the sliding action is smooth mainly depends on the torque of a slide rail, and the torque of the slide rail is generally adjusted by torque setting screws. By turning the torque setting screws inwards or outwards (tightening or loosening the screws), the torque of the slide rail is correspondingly increased or decreased. Generally, the torque set by the torque setting screws is generally factory set before the laser rangefinder is shipped to the sales points. However, after long time use, it is possible that the torque setting screws become loose. Consequently, the torque of the slide rail is decreased, and the two lens barrels may be caused to move relative to each other upon inclination, thereby resulting in undesired change of interpupillary distance. Therefore, in such a case, it is necessary for the user to manually adjust the torque of the slide rail. However, the torque setting screws are positioned inside of the laser rangefinder. This makes it difficult for the user to manually adjust the torque of the torque setting screw.
Accordingly, to overcome the above-mentioned disadvantages presented in the prior art, it is desired to provide an improved interpupillary distance adjustment mechanism for an optical device, such as a laser rangefinder.